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Vulpecula - Constellation Guide

VulpeculaVulpeculae
Vul
The Fox / The Little Fox

Introduction

Vulpecula is a small, faint constellation located in the northern section of the sky. Strangely, it was not one of the original 48 constellations created by 2nd century astronomer Ptolemy, even though the pattern of stars were clearly visible to him and other ancient Greeks and Romans.

The constellation we know today was created by Johannes Hevelius. He included it in his influential 56 page star atlas, Firmamentum Sobiescianum, which was published posthumously in 1690. Originally it was known by two names, Vulpecula cum anser and Vulpecula et Anser. The first means the little fox with the goose and the second the little fox and the goose. In his original illustration, Hevelius depicted an unfortunate goose carried in the jaws of a fox. Later the constellation was divided into two separate parts, Vulpecula and Anser. It was then re-merged into a single entity - simply named Vulpecula - by the International Astronomical Union (IAU) in the 20th century. The only remains of the goose is the constellation's brightest star, Anser (α Vul).

Locating the area of the sky where Vulpecula lies is easy; it's wedged between Cygnus and Sagitta with the western half located roughly in the middle of the well observed Summer triangle (an asterism consisting of the bright stars Deneb, Vega and Altair). For deep sky observers, Vulpecula contains the superb Dumbbell Nebula, a famous coathanger shaped open cluster and a few other open clusters. At 288 square degrees, it's the 55th largest constellation in the sky.

However this is just a chance alignment, 8 Vulpeculae is believed to lie nearly 200 light-years more distant than Anser.

Variable Star

T Vulpeculae - is a Delta Cephei type variable star located 1,672 light-years from Earth. It varies between mag. +5.41 and +6.09 over a period of 4.44 days.

Pulsar

PSR B1919+21 - In July 1967, the first pulsar, PSR B1919+21 (original designation CP 1919), was discovered in Vulpecula by Jocelyn Bell and Antony Hewish in Cambridge, England. Initially these strange pulsating signals were humorously named as Little Green Men 1, an obvious reference to some sort of extraterrestrial nature, until researchers Thomas Gold and Fred Hoyle correctly identified them as rapidly rotating neutron stars with strong magnetic fields.

PSR B1919+21 has a rotation period of 1.3373 seconds and is located 2,283 light-years away.

Deep Sky

Planetary Nebula

M27 - is the Dumbbell Nebula, a famous showstopper and must see planetary nebula. At mag. +7.4, it's the second brightest planetary nebula in the sky with only the Helix Nebula (NGC 7293) marginally brighter. Observationally, the Dumbbell Nebula is smaller than the Helix Nebula but has a higher surface brightness and therefore easier to observe. It's visible in all types of optical instruments.

A pair of 10x50 binoculars reveals M27 as a hazy small patch, located in a circular grouping of quite bright stars. Larger 20x80 models or a small 100mm (4-inch) telescope display the planetary more clearly, with the centre region slightly brighter but not distinct from the outer regions. Through medium size 200mm (8-inch) scopes, both sides of the nebula appear dimmer than the central region, revealing the dumbbell or apple core shape. A large amount of surface detail is detectable with both direct and averted vision. Even larger aperture scopes show more subtle details.

Through 10x50 binoculars, NGC 6823 is visible as a very faint glow. Larger 20x80 binoculars show the elongated shape of the cluster with the brightest stars resolvable. A medium size telescope of 200mm (8-inches) aperture brings out the oval shape with about twenty or so stars visible. Averted vision reveals more faint stars towards the cluster centre. The brightest members appear diamond or kite shaped.

The emission nebula NGC 6820 is a much more difficult object to observe and a minimum 200mm (8-inch) aperture telescope is recommended. It appears as a faint glow surrounding NGC 6823 that's more obvious when viewed using averted vision and/or a UHC filter. Larger telescopes bring out more subtle details. The best views of NGC 6820 are reserved for photographers and imagers. Here the nebula is seen in full colour with its most striking feature a larger pillar of gas and dust on the eastern side, which is similar to one of the famous pillars in the Hubble Telescope's Eagle Nebula "Pillars of Creation" image.

Open cluster NGC 6823 is about 20 light-years across and lies 6,000 light-years distance.

Open Clusters

Brocchi's Cluster (Collinder 399) - the Coathanger - is a random grouping of stars near the border with Sagitta that's best viewed through binoculars or a small / wide field telescope. The brightest 10 stars are between 5th and 7th magnitude and are arranged in the shape of an Coathanger. Six of the ten stars form an almost straight line with the remaining four shaped like a hook hanging off to the south.

At a dark site the cluster is just about visible to the naked eye as an unresolved haze. Binoculars or small size telescopes are required to reveal the Coathanger shape. Through 10x50 models it's superb, spanning about a degree in diameter with the main stars easily visible along with a splattering of fainter stars. Equally striking views are obtained in small or wide field scopes of the order of 60mm to 100mm (2.4 to 4 inch) aperture. Through larger instruments the Coathanger effect is lost slightly due to the decreased field of view, but nevertheless still interesting to look at.

The cluster was first noted before 964 by the Persian astronomer Al Sufi, which he described in his Book of Fixed Stars. Later in the 17th century, Italian astronomer Hodierna independently rediscovered it. The object was catalogued by American amateur astronomer Brocchi in the 1920s and then by Swedish astronomer Collinder in 1931.

Stock 1 - is a large binocular cluster covering an area of 1.3 degrees, which is over twice the apparent size of the full Moon. At mag. +5.3, Stock 1 is theoretically visible to the naked but difficult due to its scattered nature. However, it's a nice object that contains up to 40 stars.

NGC 6882/6885 - open clusters NGC 6882 and NGC 6885 may or may not be the same item. William Herschel discovered them on successive nights and gave almost identical descriptions. General consensus is they are the same object. To complicate the story further, Per Collinder included a small scattering of stars to the northwest edge of NGC 6882/6885 as number (Cr) 416 in his catalogue of open clusters.

NGC 6882/6885 is grouped around mag. +5.9 star 20 Vulpeculae and consists of up to 40 stars. The rough diameter of the cluster is about 20 arc minutes with the more compact cluster Cr 416 located at the northwest corner (diameter 8 arc minutes). NGC 6882/6885 shines at mag. +5.5, with Cr 416 fainter at mag. +8.1. All in all, the whole area contains a nice grouping of stars centred on bright stand out star, 20 Vulpeculae. Binoculars show the main stars and give a feeling for the area, medium and large size telescopes reveal much more. To some, the region appears as just one large group of stars.

NGC 6940 - is a nice open cluster that's easily visible in 10x50 binoculars as an elliptical haze surrounded by a few foreground stars. Larger binoculars or a small 80mm (3.1 inch) scope resolve a few stars. However, when viewed through a medium size 200mm (8-inch) instrument, it's a rewarding object. With a size of 25 arc minutes, almost as large as that of the full Moon, the cluster fills the eyepiece field of view with dozens of stars visible. Averted vision reveals fainter stars through out, with larger scopes revealing many more.

NGC 6940 is about 2,500 light-years distant and contains about 60 stars. It's not a young cluster with an estimated age of 800 million years.

NGC 6834 - is a compact mag. +7.8 open cluster about 7,000 light-years distant located at the Cygnus border. The object is visible in 100mm (4-inch) telescopes although the best views are reserved for larger instruments. In a 200mm (8-inch) reflector, NGC 6834 appears as a small rich compressed wedge shaped grouping with a V shape of bright stars at the centre. It has a diameter of 6 arc minutes with up to 50 stars brighter than mag. +15. The estimated age of the cluster is 65 million years.

NGC 6830 - at mag. +7.9, NGC 6830 is a loose cluster of at least 20 stars covering an area of 10 arc minutes. It's visible in binoculars as an unresolved haze of light. A medium size 200mm (8-inch) scope easily shows the brightest stars that are arranged in a distinct X shape. Larger telescopes reveal many more members.

NGC 6802 - When observing the Coathanger cluster with a medium / large size telescope, look to the eastern edge and you should be able to notice the faint mag. +8.8 open cluster, NGC 6802. It's easily visible through a 200mm (8-inch) telescope, appearing as a line of about 10 faint stars extending in a north-south direction. Using averted vision, the cluster appears more pronounced with fainter stars visible. With a large 350mm (14-inch) telescope the oblong nature of the cluster is more prominent and more stars are visible.